1. Field of the Invention
The present invention relates to a method of forming an armature core of an electric rotating machine. More particularly, the present invention pertains to a method of forming a core sheet used for constituting an armature core.
2. Description of the Prior Art
The armature core of an electric rotating machine has heretofore been formed by a process of axially stacking a multiplicity of core sheets. As shown in FIG. 6, each core sheet 1 which is conventionally used for forming an armature core has the shape of an annular disk, and the radially outer portion of the core sheet 1 is provided with a multiplicity of armature coil winding slots 2 which extend radially inward, are circumferentially spaced at equal intervals and into which armature coils are to be set. The radially inner portion of the core sheet 1 is provided with a multiplicity of relatively long and narrow grooves 3 which extend radially outward. As will be clear from FIG. 6, each armature coil winding slot 2 formed in the core sheet 1 generally has the shape of the letter "V" and its opening portion 2a is somewhat narrowed. In general, such core sheet 1 is formed of a band-shaped metal sheet 4 such as that shown in FIG. 5. The metal sheet 4 has notches 2' and 3' respectively formed along two longitudinal edges thereof, in advance, the notches 2' and 3' corresponding to the slots 2 and grooves 3 of the core sheet 1, respectively.
The band-shaped metal sheet 4 is formed into the annular disk-shaped core sheet 1 by a process of winding the sheet 4 around a mandrel 5 (see FIG. 2) with one turn. The notches 3' allow the sheet 4 to be bent with no difficulty because they get narrower as the sheet 4 is bent, and with a high degree of accuracy because they engage with projections 6, respectively, which are formed on the mandrel 5.
In the above-described conventional core sheet 1, the grooves 3 which have engaged with the projections 6 on the mandrel 5 remain as shown in FIG. 6 after the process is completed. Accordingly, when an armature rotary shaft (not shown) is press-fitted into the central bore of the core sheet 1 to thereby secure the core sheet 1 to the rotary shaft, such grooves 3 cause a reduction in the area of contact between the core sheet 1 and the armature rotary shaft, resulting in a reduction in the frictional force therebetween thereby inhibiting firm press-fitting of the armature rotary shaft into the central bore of the core sheet 1.